Without limiting the scope of the invention, the background will describe the satellite based global positioning system, as an example.
The satellite based global positioning system (GPS) includes twenty-four satellites, orbiting 11,000 miles above the surface of the earth that emit signals to receivers below. By measuring the travel time of a signal transmitted from each satellite, a receiver can calculate its distance from that satellite. Satellite positions are used by a receiver as precise reference points to determine the location of a receiver. When receiving the signals from at least four satellites, a receiver can determine latitude, longitude, altitude and time, each of which are necessary in the navigation of an aircraft. The basic GPS service provides users with approximately 100 meter accuracy ninety-five percent of the time anywhere on or near the surface of the earth.
The benefits of satellite navigation over those of traditional navigation systems are significant. Satellite based systems achieve greater accuracies than most existing land based systems because the satellite signals are propagated independent of the ground making the system less prone to ground derived errors. Furthermore, because the satellite signals are available worldwide, GPS represents an unique opportunity for the international aviation community to start converging toward the goal of a single, integrated Global Navigation Satellite System (GNSS).
GNSS will eventually allow aviation users to reduce the number of different types of receivers required for navigation services for all phases of flight. Coupled with satellite communications, satellite based navigation will contribute to increased safety and efficiency of international civil aviation by supporting real time surveillance of aircraft and reducing the separation requirements.
The transition from various ground based systems to a common satellite based navigation system on a worldwide scale will require tremendous cooperation among international civil aviation authorities, governments, and industry representatives. The FAA is involved in such a transition on a national basis and has made the commitment to move from its own extensive ground based communications, navigation and surveillance system to one which will rely primarily on satellite navigation. This transition will not only prepare the U.S. National Airspace System (NAS) to meet the demands placed upon it by ever increasing aviation operations, but will serve the goals of the international community by beginning the transition to a seamless worldwide global satellite navigation system.
The FAA began the transition to GPS based navigation in 1994 with the approval of GPS as a supplemental navigation aid for en route through nonprecision approach phases of flight. This was followed by approval of GPS as a primary means of navigation in the oceanic environment as well as for remote operations. These two operational approvals are contingent upon the use of a properly certified Technical Standard Order (TSO) C129A GPS receiver which includes the Receiver Autonomous Integrity Monitoring (RAIM) feature to verify system integrity. In addition, to support this capability, GPS procedures were developed.
The next significant step in the FAA's transition to satellite based navigation is a Satellite Based Augmentation System (SBAS) called the Wide Area Augmentation System (WAAS) WAAS will satisfy the FAA requirements to be used as the only radio navigation aid for all flight operations down to and including Category 1 precision approaches. WAAS alone will not satisfy the FAA requirements for Category 2/3 precision approaches, nor will it satisfy the requirements for Category 1 approaches outside the WAAS coverage area.
For this reason, the FAA is also planning to implement a Ground Based Augmentation System (GBAS) called the Local Area Augmentation System (LAAS). LAAS is intended to satisfy FAA precision approach requirements for accuracy, availability, and integrity in order to provide Category 1 precision approach capability where the WAAS cannot, as well as Category 2/3 precision approach capability. In addition, the LAAS signal allows the user to have highly accurate position information anywhere in the airport vicinity, enabling the potential use of LAAS as an all weather surface navigation sensor and an input to surface surveillance/traffic management systems.
It has been found, however, that even with the implementation of the LAAS, only aircraft in the vicinity of an airport will be able to perform Category 2/3 precision approaches. Thus, for such precision approaches of, for example, helicopters or tiltrotors, in areas not covered by the LAAS, a need has arisen for a method and system for utilizing GPS to create a precision approach procedure to a position on the ground using onboard equipment.